


You Are Filled With Lust

by Infinite_Volume



Category: Undertale (Video Game)
Genre: Breaking the Bed, Cum Inflation, Deepthroating, F/M, Growth, Incest, Large Breasts, Large Cock, Orgasm, Penis In Vagina Sex, Penis Size, Size Difference, Size Kink, Squirting, Threesome, Threesome - F/M/M, Vaginal Sex, excessive cum, hyper, hyper cum
Language: English
Status: Completed
Published: 2018-09-01
Updated: 2018-09-01
Packaged: 2019-09-20 10:03:28
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,749
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17020593
Author URL: https://archiveofourown.org/users/Infinite_Volume/pseuds/Infinite_Volume
Summary: Frisk and Asriel share some very interesting drawings with Toriel. Through the power of Determination, the three of them resolve to make the fantasies expressed by the human creators of these drawings a reality. What better way to integrate into human society than by sharing in their erotic desires?(There are actually very many ways that are infinitely better than that.)





	You Are Filled With Lust

Since Frisk’s return to the surface, mysterious and powerful old magics have been reintroduced to humankind. Having long since traded witchcraft for modern science, the wave of mystical beings and arcane knowledge that poured out of the Underground turned human society on its head. More powerful than Alphys’s tech or Toriel’s wizardry, however, was the power of determination: A power innate to all humans but mastered by very, very few. Close to zero humans were even aware that they had this power.

Frisk was an exception to this. He knew.

Frisk, who spent such a long time in the Underground, became the first human in the modern age to fully realize determination’s power. Of course, Frisk used this power not to spread violence, but to breed love.

He and Asriel both ended up keeping in contact with each other after the barrier was broken, exchanging cultural artifacts and plotting up ways to get more humans to visit the Underground. Tourism has been fairly one-sided in favor of the humans, after all…

One night, Asriel and Frisk approached Toriel with an idea.

“A-Asriel?! What’s gotten into you?”

Toriel sat up in her cozy little loveseat, reading glasses on and with a human cookbook open to dessert recipes laid on her lap. She’d looked up when she was blind sighted by her son’s proposal.

“Frisk and I both think it’d be a great idea! Right, Frisk?”

Frisk looked as placid as ever, though his unwavering stare into Toriel’s eyes somehow felt like a  _yes_.

“We need to show the humans that monsters can be their friends,” Asriel continued. “Frisk showed me these stories and drawings from the surface…A lot of people  _really_  like monsters!”

“What kinds of drawings, Azzy?”

Frisk held up a finger, signaling Toriel to “wait up a moment.”

He rustled through his backpack, pulled out a laptop computer, opened it up, and executed a few quick clicks and keystrokes. Asriel watched the screen as Frisk navigated his hard drive.

“Aah! This is the one!” Asriel shrieked in excitement. “Show Mom, Frisk!”

Frisk turned his computer around, revealing the brightly lit screen to his goat-like guardian.

“O-oh my…”

Toriel stared intently at an image of two small looking boys, short in stature but hung like whales, clinging tightly to a massive goat-gal. Enormous breasts, killer thighs, and a belly thrice the size of a minivan. Both of the boys, human in every respect but their monstrous cocks, were inserted so deeply in the monster girl that you could see the outline of their glands though her cumflated stomach. The girl looked ecstatic to be bred by such virile cuties. This image was beyond anything Toriel had ever even thought possible. Who would illustrate such a thing? Why would they do it?

…

Do they really think anthro goats are attractive?

Asriel broke the silence in the room.

“Don’t you think she looks like you, Mom?”

“A little…”

Her white, furred face was starting to turn pink.

“We need to show humans everywhere that there are monsters just like this in the Underground! I’m sure more will want to come visit us then!”

“So…you want to…r-recreate pictures like this?” Toriel asked her son.

“Mhm! As videos!” He responded enthusiastically.

Toriel had two minds about the situation. Part of her knew just how strange and taboo it would be to oblige, and to have the whole thing taped and intentionally broadcast to humanity. Another part of her, however, pushed her deeper down the hole of depravity. She hadn’t felt the same type of love as the monster in that drawing in a very, very long time. Seeing a picture like that, inspired by the wildest sexual fantasies of a person she’d never met, made her wonder if a human could ever think of her the same way. Could they love her tall, imposing frame? Her long face and white coat of fur? Her fat tits and enormous hips?

It had been so long since anyone had looked at her as a sexual object. She had forgotten what it felt like.

“If you’re sure it’s for the best, Azzy…”

“Alright!” Asriel’s stubby tail started wagging so fast that Frisk felt a light breeze just from standing behind him.

The two boys hurried Toriel over to her bedroom. They’d already set the cameras up in advance…as if they knew she’d approve.

“Come on,” Asriel called out as he shoved his mom back-first onto her comforter, “Frisk, show her what you showed me!”

Toriel’s turned her attention over to Frisk, who was still standing in her bedroom doorway. Frisk undid his pants, tossed them aside, and pulled a flaccid, 7-inch snake out of the hole of his underwear.

She was in shock at the size of it, especially in relation to the rest of his body.

“O-oh…It’s so big.”

“Watch, Mom! He’s about to show you!”

“ _Hmm…?_ ” Toriel pondered for a second. “ _Isn’t it already out?_ ”

Frisk grabbed ahold of his shaft with a single hand and started stroking vigorously. He was still totally soft, so it flopped around everywhere for the first couple of seconds before taking in any blood. The thwacks and smacks of cock-meat against thigh bounded off the walls of the otherwise silent bedroom. His inner-thigh turned a little pink from the haphazard thwacking. Little drips of precum splattered across the room, striking Toriel in the cheek.

The soft, spongy flesh of his cock filled with blood. 7 inches, then 9 inches, then 12 and 15 and 28…Length shot out of Frisk like a spring. His girth multiplied too, making it so that he couldn’t even cup a quarter of his rod at a time.

Still not entirely hard, Frisk let his dick fall out oh his hand. It hit the floor with a mighty thud, shaking the foundation of the house and rocking their bed. He stood there triumphantly, hands on his hips and with his pelvis thrust a little bit forward.

Toriel shrieked in surprise. Her pink face was as red as a beat.

“ _It’s twice as big as Gorey’s…_ ” she whispered to herself.

“E-hehe,” Asriel chuckled. “Look, I can do it too!”

Asriel had his package out of his pants before Toriel could even process what he’d just said. Suddenly, she was staring down another half-footer and a pair of big, fluffy, plum-sized testicles. They were inches from her face. She could smell the musk lifting off of them.

Asriel put one hand on his shaft and another on his mothers’ head. He rubbed them both, but with less vigor and intensity than Frisk had. His cock, too, exploded in size. Toriel was so close that she could hear the her son’s pulse through his inflating meat. At about the 2-foot mark, Asriel backed up to line his dick up with her crotch. He quickly removed her panties and cast the skirt of her tunic to the side. He plopped his heavy penis down against her mound, applying a wonderful kind of crushing pressure: not too light, but not too heavy. It made Toriel squirm.

“Mmmhm–” Asriel started squirming a bit himself; the feeling of an endlessly progressing erection was one he loved, but still wasn’t quite used to. “L-look…my thing already reaches all the way up to your boobs!”

The head of his cock laid right between Toriel’s melon-sized tits. His glans looked right at home there…Just as large, just as bulbous, and still just was wobbly. For all the growing he’d already done, it was clear that Asriel had a lot more to do as well.

“Uhm…When did you boys get this big?”

“Frisk and I are just really…determined! We want to make you feel good, and to show the humans what they want to see!

Frisk had started walking up to the bed. He climbed atop the headboard and laid his mammoth trunk on Toeirl’s face. The heat emanating off of it made he sweat, and the weight of it on her chest was oddly comforting. Both of their glans met at her bustline, drooling slime all over her tits and each other’s dicks.

The sight and sensation of the two lads, so mature and well developed, fills Toriel with lust.

After a few seconds of awkward silence, feeling the pulsating, slowly growing penises of her son and his best friend against her torso, a single word fought its way out of her squeaking mouth.

“Well…?”

The boys didn’t respond, looking and smirking at each other instead as they continued to rub their monstrous tools.

“ _Well,_ ” she repeated, “C-Can we start?”

The monster-human duo needn’t wait any longer. They were bursting with energy too, after all.

Frisk was the first to take action, lifting his hefty member up and dangling it right above Toriel’s nose. She opened wide and stuck her tongue out. She tasted the salty pre and tender flesh of his cock as he began lowering it into her throat.

“ _PFFF-GLURK!_ ”

His penis got stuck part way down her esophagus. He hadn’t even put an entire foot in her yet, and she was already at her normal limit. Not content to stop there and simply make do, Frisk started to push and shove himself down the goat-gal’s throat. Immense determination to fit his immense shaft down her gullet welled up inside Frisk; every lurch he made forward allowed at least an extra inch of his length to enter her sticky, tight gorge.

“Ha! I can see the shape of yours doing down her neck, Frisk!” Asriel seemed amused by it all.

Toriel’s body started shaking violently. Her cunt started spraying a fine mist of girl juice all over the underside of her son’s cock. He pussy dilated, gaping and grasping at nothing, hungering for the cock right in front of it. Just the feeling of Frisk’s manhood in her made her that much more excited to receive Asriel’s. Somehow, she still found the power to breathe and stay conscious despite the fact that she had a penis the width of an oak tree stuffed down her windpipe.

Lust, maybe?

“Hehe…Now that mine is all nice and lubed up, I guess I should put it in too…”

Frisk flashed a thumbs-up at Asirel as the short boss-monster scooted on his butt towards the foot of the bed. He had to move back quite a ways just to line the tip of his dick up against Toriel’s lips.

When her lips did finally kiss his glans, they practically swallowed him up right away. Toriel’s labia instantly parted to accommodate his basketball-sized head. The rest of his entry into her lovely depths was quick and easy – perhaps Frisk’s efforts had an effect on her body, or her own lust to take in all of them had given her a power not unlike the boys’ determination.

As the two of them delved deeper into their goat mom, her abdomen stretched to unbelievable levels to accommodate their buried lengths. They could feel their heads slide past each other again, this time separated by a film of gooey, flexible internals. As both Frisk and Asriel finally hilted themselves in Toriel, they reached across her body and grabbed each other’s hand. Frisk was seated on her face, huge and hefty balls squashed up against her eyes like goggles, and Asriel had his face buried between her wobbly orbs. All three of them were wrapped in an extreme ecstasy, but neither of the boys were anywhere near finished yet. Toriel was drowning in multiple orgasms and convulsing like a mad woman, but neither Frisk nor Asriel had even cum yet.

“Hey Frisk!” Asriel shouted.

Frisk cocked his head in curiosity.

“I bet you I can cum more than you can! More than in that picture, too!”

Frisk let go of Asriel’s hand and flashed him a thumbs-up. He figured there wouldn’t be any way he’d lose to Asriel. That boss monster was an unusually strong one, even given all his years in the Underground, but Frisk was stronger  _and more determined_. A human would never lose to a monster in this sort of competition. It was the wonderful, wonderful, wonderful human mind that drew that image and it would be a delicious, tremendous, beautiful human cock that would it a reality.

Asriel, as friendly as he was with Frisk, wasn’t going to lose without a fight. Monsters, naturally, have the most monstrous orgasms!

Both of their sacks swelled and rumbled, filling with cum that seemed to materialize out of thin air. There was no possible way to scientifically explain the sheer weight and volume of sperm brewing in their testes. There might not even be a way to quantify it.

Feeling his coming orgasm, Frisk poured additional power into his already telephone pole-like cock. It Doubled, tripled and quadrupled in size, overtaking the boundaries of the bed they were all laid atop and pushing Asriel on his back.

Asriel, too, started growing again. Feeling the crushing weight of his opponent’s member against the walls of his mom’s quivering cunt, Asriel’s comparatively fun-sized dick swelled up to match. The curvature of his pink pole made for an otherworldly and marvelous bulge, jutting out from between her breasts and shooting beyond Frisk’s perpetually shut eyes.

“Frisk! Mom! I…I can feel it!” Asriel shouts were muffled by the hyper-sized bulge of Frisk’s that pinned him against the bed. The gurgling roars of his balls, however, carried. They communicated the exact same message Asriel was trying to shout: that he was about to cum.

Frisk was close too. The both of them continued to grow, bursting with extra feet worth of length and girth with every passing second. They’d long outclassed the two boys in the image they’d shown earlier, effortlessly exploding past the limits of even the most size-hungry artist’s wildest imagination. Their cocks rubbed up against the walls of the room they were in, creating cracks in the wall and irreparably damaging the structural integrity of their house. The potential destructive force of their dicks were outweighed only in their capacity to deliver pleasure, with Toriel as their sole recipient. Her shaking intensified, sending vibrations of all different wavelengths down their shafts until finally…

_SPLOOOOOOOOOOOOOOOOORRRFFFPTHHH!!!_

_BLGOOOOOOOOOOOOHHGFFFFSHHHHH!!!_

Her poor, tiny tummy inflated to the size of a blimp in the matter of seconds – her light-speed filling was entirely the doing of Frisk. Her womb, too, was inflated to beyond the size of her entire home – Asriel alone had the pleasure of doing that job. The two bloated organs, converted entirely into cavities solely for the purpose of storing cum, were indistinguishable from the outside. Toriel just looked like one massive, squishy mountain of fur and cum.

Having reduced their brand-new, tiny home to a bunch of rubble and dust, Frisk and Asriel were lifted high above the ceilings of every house within view. They were still in the underground, but the cave’s own ceiling never looked to close.

Frisk was still shooting goo out at an impossible rate, adding the volume of a truck to Toriel’s gut with the snap of a finger. Asriel was also still cumming wildly, egged on to orgasm even harder by the mind-melting sensation of the waterfall of his own jizz washing over his body and into every crack and crevice. He could feel his own slimy seed worm itself in between his toes, his fingers, and under his pits. Never before had he ever even dreamed of pleasure like this. Even with all that pressurized cum shooting out of her pussy, Asriel was still filling his mom with multiple times that amount at every moment.

Toriel kept silently wishing for more. More, more, more! She wanted Frisk to win their lovely little wager, and she wanted Asriel to win too! No matter who lost, she was sure she’d be the winner because she already was!

Frisk and Asriel could feel Toriel’s resolve: the strong will of a boss monster pushing them to go further. The two boys doubled down on both their growth and on their output, accelerating their ascent to the roof of the Underground.

The ceiling came closer, and Frisk kept cumming.

The ceiling came closer, and Asriel kept cumming.

Closer, closer, and closer still. Toriel’s body was truly enormous, and neither of the boys showed any signs of slowing down.

Just before crashing through the ceiling, Toriel had a thought…

“ _Oh my…I hope the humans really_ do  _like this sort of thing!_ ”


End file.
